FIG. 2 shows this kind of a conventional exhaust gas processing apparatus.
When a semiconductor manufacturing equipment 1 is in the film forming step, an exhaust gas mainly containing SiH4 as a residual raw material gas is discharged from the semiconductor manufacturing equipment 1. Also, when the semiconductor manufacturing equipment 1 is in the cleaning step, an exhaust gas mainly containing NF3 as the residual cleaning gas and SiF4 produced by cleaning is discharged from the semiconductor manufacturing equipment 1.
The number of the semiconductor manufacturing equipment 1 is not limited to one and plural equipments may be sometimes provided. Sometimes, a portion of the equipments may be in the film forming step and others may be in the cleaning step.
The exhaust gas from the semiconductor manufacturing equipment 1 is transferred to a combustion-based detoxifying device 3 by a vacuum pump 2. In case plural semiconductor manufacturing equipments 1 and vacuum pumps 2 are provided, each exhaust gas from plural semiconductor manufacturing equipments 1 is transferred to the combustion-based detoxifying device 3 by each vacuum pump 2.
The combustion-based detoxifying device 3 delivers the above exhaust gas into flame formed by a burner such as an air burner or an oxygen burner thereby oxidizing and decomposing the above harmful components in the exhaust gas.
When the semiconductor manufacturing equipment 1 is in the film forming step, SiH4 contained in the exhaust gas is converted into SiO2 and H2O in the combustion-based detoxifying device 3. Also, when the semiconductor manufacturing equipment 1 is in the cleaning step, NF3 contained in the exhaust gas is converted into HF and NOx, while SiF4 is converted into SiO2 and HF in the combustion-based detoxifying device 3.
Therefore, the exhaust gas to be discharged from the combustion-based detoxifying device 3 contains SiO2 and HF as a substance to be removed. This exhaust gas is then fed into a dust collector 4 such as a bag filter, where SiO2 in the form of solid particles is collected.
In the case of collecting SiO2 in the dust collector 4, SiO2 in the form of solid particles is collected on a surface of a filter, and is gradually accumulated with inflow of the exhaust gas. Since the exhaust gas contains HF, a portion of this HF reacts with SiO2 to produce a small amount of SiF4 again.
The exhaust gas containing HF and SiF4 from the dust collector 4 is sucked by a blower 5 and fed into a gas cleaning device 6. This gas cleaning device 6 is also called a wet type scrubber and causes gas-liquid contact between an alkali cleaning solution such as an aqueous sodium hydroxide solution, and an exhaust gas thereby removing. HF as an acidic gas and SiF4. It is also possible to increase removal efficiency by optionally providing this gas cleaning device 6 with a two-stage constitution.
The gas exhaust gas to be discharged from the cleaning device 6 is diffused into the atmospheric air through a blower 7 after confirming that the content of a harmful component is reduced to the regulation value or less.
By the way, in such a processing method, SiF4 in the exhaust gas is hydrolyzed to produce SiO2 and HF in the gas cleaning device 6, and HF is converted into NaF through a reaction with sodium of an alkali cleaning solution. There is a disadvantage that since SiO2 and NaF are solid substances, these substances adhere and accumulate to a filler inside the gas cleaning device 6, and the interior of a mist separator and a cleaning solution circulation pump, thus causing clogging of the gas cleaning device 6 and pump failure.
Therefore, in a conventional device, it was necessary to frequently overhaul a gas cleaning device 6 body and a circulation pump.